From, for example, U.S. Pat. No. 3,999,895 (Bede Alfred Boyle) a hydraulically driven pump means is previously known, in which several axial cylinder spaces in a rotor are arranged concentrically and comprise drive pistons which are each connected to a pump piston. At one end of the pump means, a driving fluid is supplied and discharged, and at the other end a pump flow is supplied and discharged. Other technical solutions involving several conically arranged cylinder spaces in a rotor in which, in each cylinder space, a drive piston is connected to a pump piston, are also previously known from U.S. Pat. No. 4,500,261 (Ode, Tornblom). When the motor is driven round, the hydraulic pressure influences the drive piston, connected to the pump piston, for pumping of a flow.